This invention relates to a burn-in system for screening semiconductor devices such as ICs (integrated circuits) by operating the devices under accelerated aging conditions for some period of time while monitoring the behavior of each device.
In the inspection of industrially manufactured ICs a burn-in procedure is widely employed as a screening test to eliminate early failures from the devices supplied to customers. Burn-in is performed after completion of the IC fabrication process, that is, after resin encapsulation of individual IC chips mounted on leadframes. In a dynamic burn-in procedure the ICs to be screened are kept at a predetermined high temperature for a prescribed period of time to accelerate aging, and an operational current and driving signals are applied to the ICs under the specified accelerated aging conditions.
For burn-in testing of ICs a recent trend is to employ a monitored burn-in system which includes monitoring instruments for examining whether or not the operational current and driving signals are being properly applied to each of ICs under accelerated aging and whether or not each IC is operating properly. The employment of monitored burn-in systems will enhance the reliability of burn-in procedures.
For a burn-in procedure it is important to appropriately set the duration of burn-in. In the practice of burn-in of ICs with a conventional burn-in system which may or may not be monitored, the burn-in duration is set based on the results of preliminary testing on the same type of ICs. The preliminary testing is for the purpose of examining a correlation between accelarated aging time and a cumulative failure rate of the ICs under accerated aging to determine the time by which the cumulative failure rate reaches saturation, and in compliance with the saturation time the duration of the actual burn-in procedure is set.
The correlation between accelerated aging time and the cumulative failure rate is specific to each type of IC. Therefore, to perform burn-in test of various types of ICs it is necessary to collect failure rate data for setting an appropriate burn-in duration for each type of IC. The data collecting work requires much time and labor. Furthermore, for any type of IC the burn-in duration determined by this method is not always appropriate since there is a possibility that the quality level of the IC products varies by fluctuations of the manufacturing process conditions. If the duration of accelerated aging is inappropriate a burn-in procedure cannot be regarded as a really effective screening method for the guarantee of the reliability of IC products.